This invention relates generally to a combination accumulator and variable volume sump, in particular an accumulator and sump utilized in a vehicle anti-lock brake system.
A vehicle anti-lock brake system may include a pump for transmitting pressurized fluid throughout the system, including the displacement of fluid into an accumulator and the removal of fluid from a sump. The sump is present in the system in order to provide a mechanism which will quickly absorb fluid being displaced from the brakes during a decay function. The fluid is displaced through line connections and into the sump, and then the pump is actuated shortly thereafter to draw fluid from the sump and transmit the fluid into the system which includes an accumulator where pressurized fluid may be stored. If a large amount of fluid has been displaced through the brake system to the brakes, such as occurs during a high-pressure "spike" application of the brakes, during the decay function the fluid in the brakes is displaced to the sump which will absorb a predetermined amount of fluid volume established by failure mode considerations. The remaining excess amount of fluid from the brakes must be pumped into the accumulator to permit complete release of the brake pressure. The accumulator has a gas precharge pressure which is substantially higher than normal braking pressure. In order to reduce rapidly the fluid braking pressure, the pump must displace a considerable amount of fluid. For a large volume fluid flow to be effected by the pump at the high precharge pressure of the accumulator, the pump motor requires a substantial amount of horse power and a correspondingly large electric current requirement. It would be desirable to provide a sump displacement which could absorb the excess amount of fluid displaced during the decay function so that the pump need not displace the excess fluid volume to the accumulator, and thus utilize a much smaller pump. It is also highly desirable that in the event of some failures, such as failure of the pump, that the sump absorb a small volume of fluid so that only a modest portion of available master cylinder fluid displacement will be "lost" into the sump.